Vulcanization of elastomeric compositions



United States Patent 3,370,051 VULCANIZATION 0F ELASTOMERIC COMPOSITIONS Frank A. V. Sullivan, Westfield, and Arthur C. Lindaw,

Bridgewater Township, Somerset County, NJ., assignors to American Cyanamid Company, Stamford, Conn., a corporation of Maine N 0 Drawing. Continuation-in-part of applications Ser. No. 176,435, Feb. 28, 1962, and Ser. No. 282,856, May 24, 1963. This application Jan. 25, 1966, Ser. No. 522,821

7 Claims. (Cl. 26086.l)

This application is a continuation-in-part of application Ser. No. 282,856, filed May 24, 1963, now abandoned; and the latter is, in turn, a continuation-in-part of application Ser. No. 176,435, filed Feb. 28, 1962, now Patent No. 3,215,703.

The present invention is concerned with the vulcanization of chlorine-containing synthetic elastomers and with a new class of accelerators for that purpose. The invention also contemplates new compounds of this class and both vulcanized and vulcanizable compositions containing the same.

In general, the novel accelerators of the invention may be defined as 2-thiazolidinethiones of the structural formula:

wherein R may be an alkyl, cycloalkyl, aryl, aralkyl, furfuryl or morpholinoalkyl; and

wherein R may be an alkylene, cyclohexylene or phenylene.

Chlorine-containing synthetic elastomers with which the present invention is concerned include several different commercially available types. Polychloroprene polymers represent one such type. As used herein, the term polychloroprene includes not only polymers of chloroprene (2 chloro 1,3 butadiene), but also copolymers thereof with polymerizable vinyl or diene compounds wherein chloroprene is the predominant monomer.

Other types of chlorine elastomers which may be used in the vulcanization process of this invention include, for example, chlorinated butyl rubber; polymers of chlorinated and/ or chlorosulfonated polyethylene; copolymers of ethyl acrylate and vinyl chloracetate; copolymers of ethyl acrylate and 2-chloro-ethyl vinyl ether and the like.

Various elastomers of these types containing reactive chlorine atoms have one property in common. It is the property of being vulcanizable, at least in part, by crosslinking through the reactive chlorine atoms. Such elastomers also may be curable by cross-linking through carbonto-carbon double bonds. In any case, the Z-thiazolidinethiones of the present invention have shown useful properties as assistants in the vulcanization of these active chlorine-containing elastomers.

However, since polychloroprenes present the typical problems with which this invention is concerned, they will be initially discussed as the illustrative elastomers. Commercially these polychloroprene polymers and copolymers are available under a variety of type designations, usually grouped as general-purpose types or specialty types.

General-purpose polychloroprenes or neoprenes also usually are grouped in two classes, the sulfur-modified and the non-sulfur-modified types. Sulfur-modified neoprenes, such as types GN, GN-A and GRT, require only metallic oxides for vulcanization, since they contain sulfur or such sulfur compounds as thiuram disulfide. In contrast, non-sulfur-modified neoprenes, such as types W and WRT, have a more uniform molecular structure and do not contain sulfur, thiuram disulfide or other compounds capable of decomposing to yield either free sulfur or a vulcanization accelerator. They require not only metallic oxides, but also accelerators to develop proper cures.

Neoprene types W and WRT, for example, are normally formulated with a metallic oxide such as magnesia or zinc oxide. An accelerator still is generally necessary to provide acceptable curing characteristics and vulcanizable properties. Many commercially-available rubber accelerators, such as the thiazoles and the unsubstituted thiazolines, have very little practical value as active accelerators for polychloroprenes such as type W. Others, such as most dithiocarbamates, are too active and have serious scorching tendencies. Among the accelerators useful for other purposes which have been proposed for the purpose include such widely varied materials as:

diorthotolylguanidine salt of dipyrocatechol borate ethylene thiourea tetramethylthiurammonosulfide salicylic acid butyraldehyde-aniline condensate butyraldehyde-mono butylamine condensate ethyl chloride, formaldehyde, ammonia reaction product diphenylguanidine plus sulfur In general, they either do not provide the desired vulcanizate or they are too scorchy. The most generally useful and perhaps most effective has been found to be 2- merca-ptoimidazoline (ethylene thiourea). However, it too has not proved wholly satisfactory, its scorch tendencies being too high.

Surprisingly, compounds of this invention are found excellent as accelerators for polychloroprenes. They give safe processing of neoprene types W and WRT. They have a markedly delayed action and therefore do not cause premature vulcanization or scorching. Physical properties of resultant vulcanizates are comparable to those obtained by the use of ethylene thiourea. The scorching time is considerably extended over that provided by ethylene thiourea.

Accelerators of this invention may be prepared by several difierent general procedures. In the first, carbon disulfide is reacted directly with an N-substituted betaaminoethanol, presumably according to the reaction In the second method, a modification of the first, carbon disulfide is first reacted with aqueous potassium hydroxide and ethanol, and the resulting xanthate is reacted with an N-substituted beta-aminoethanol, presumably according to the reaction CHzOH In a third method, ethylene dibromide is reacted with a diaryl thiourea and the resulting 3-aryl-2-aryliminothiazolidine is then reacted with carbon disulfide.

In accordance with these methods, the following 3- substituted Z-thiazolidinethiones may be prepared and used in the practice of the present invention:

.3,3'-methylene-bis(2-thiazolidinethione) 3,3'-propylene-bis(2-thiazolidinethione) 3,3' butylene-bis(Z-thiazolidinethione) 3,3-ethylene-bis (Z-thiozolidinethione) 1,4-cyclohexylene-bis (2-thiazolidinethione) 1,4-phenylene-bis(2-thiazolidinethione) *These are believed to be new compounds.

Accelerators of this invention may and will be used tenders, reinforcing materials and carbon blacks, and,

fatty acids and lubricants. Additionally, various metal oxides may be added for the various functions which they are capable of serving. Zinc oxide may be used as a curative. Other alkaline earth oxides such as magnesium, barium and calcium oxides may be added as acid binders.

In practice, the amount of accelerator which may be used with the chloroprene polymer stock may be varied within quite wide limits, according to the result desired. In general, from about 0.1% to about 2.5% of the accelerator based on the weight of the chloroprene polymer is employed. In black stocks it is generally preferable to use from about 0.25% to about 1.25% of the accelerator based on the weight of the chloroprene polymer present in the stock to be vulcanized and in general this will be found to be good practice. In general, for white stocks somewhat larger amounts, usually from about 0.5% to 2.5 will be employed.

4 Typical polychloroprenes, such as types W and WRT, usually are compounded by milling together the ingredients. For optimum activity of the 3-substituted 2- thiazolidinethiones, it is desirable that the order of addition of the ingredients be that shown in the examples.

This procedure will be further described in conjunction with the following illustrative examples. Therein all parts and percentages are by weight unless otherwise noted and all temperatures are in degrees centigrade.

To illustrate preparation of compounds of this invention, the following several examples of the production of new compounds are given.

Example 1.3-(p-Methylbenzyl)-2-thiaz0lidinethi0ne HzU-N HsC-S Add 30.7 parts of Z-(p-methylbenzylamino)-ethanol to 31.5 parts of carbon disulfide with external cooling. The resulting mixture is heated in an autoclave at 140 C. for 4 hours. The colorless, crystalline product obtained by crystallization of the crude product from alcohol melts at about 113 C.

Analysis.-Calcd. for C I-1 N5 2 C, 59.3; H, 5.83; N, 6.28; S. 28.7. Found: C, 59.3; H, 5.56; N, 6.34; S, 29.0.

Example 2.3-(p-Meth0xybenzyl)-2-thiaz0liclinethi0ne HzC-N HzC-S Add 42 parts of 2-(p-methoxybenzylamino)-ethanol to 44.2 parts of carbon disulfide with external cooling. The resulting mixture is heated in an autoclave at 140 C. for 5 hours. The colorless crystalline product obtained by crystallization of the crude product from alcohol melts at about 104 C.

Analysis.Calcd. for C H NOS C, 55.2; H. 5.44; N, 5.86; S, 26.8. Found: C. 55.3; H. 5.36; N, 5.80; S, 27.1.

Example 3.3-ethyl-2-thiazolidinethi0ne H2C-N To a solution of 20.3 parts of potassium hydroxide in 133 parts of anhydrous ethyl alcohol, add with stirring 81.5 parts of carbon disulfide. To the resulting yellow slurry, add with stirring and cooling, 89 parts of 2- (ethylamino)ethanol. The resulting mixture is then refluxed for about 16 hours. After removing the solvents by distillation from a steam bath, the insoluble material is removed by filtration. The crude oily product (filtrate) is fractionated by distilling in vacuo, and the portion boiling at approximately 135136 C. at 1 mm. pressure is collected. The product is a light yellow, viscous oil.

Analysis.-Calcd. for C H NS C. 40.8; H, 6.1; N, 9.5; S, 43.5. Found: C. 41.0; H, 6.18; N, 9.38; S, 43.6.

Example 4.3-(beta-hydroxyethyl)-2-thiaz0lidinethione A mixture of 210 parts of diethanolamine and 304 parts of carbon dissulfide is heated in an autoclave at C. for 4 hours. After extracting the product twice with 250 parts of water, the residue is purified by a vacuum distillation. The product, boiling at 213219 C. at a pressure of 7 mm. of mercury, is a light yellow oil.

Analysis.Calcd. for C H NOS C, 36.9; H, 5.5; N, 8.6; S, 39.2. Found: C, 36.4; H, 5.68; N, 8.44; S, 40.7.

Example 5.-3-(beta-methoxyethyl)-2-thiazolidinethione CHzCHzO CH3 HzCN HzCS

A mixture of 21.4 parts of Z-(beta-methoxyethylamino)ethanol and 21.7 parts of carbon disulfide is heated in an autoclave at 140 C. for 4 hours. The reaction mixture is distilled in vacuo. The product is a yellow oil boiling at about 173175 C. under a pressure of 3.5 mm. of mercury.

Analysis.Calc-d. for C H NOS C, 40.7; H, 6.2; N, 7.9; S, 36.1. Found: C, 41.9; H, 6.1; N, 8.14 S, 30.1.

The intermediate, 2-(beta-methoxyethylamino)ethanol is prepared by reacting the p-toluenesulfonyl ester of beta-methoxyethanol with monethanolamine in the presence of sodium hydroxide at 130 C. The compound boils at 99-103 C. under a pressure of mm. of mercury.

Example 6.--3-cycl0hexyI-Z-thiazolidinethione C Hz HzCI T /C=S HzC-S A mixture of 71.5 parts of 2-(cyclohexylamino)ethanol and 76 parts .of carbon disulfide are heated in an autoclave at 138140 C. for 4 hours. After crystallization from ethanol, the colorless crystalline product melts at 120120.5 C.

Analysis.-Calcd. for C H NS C, 53.8; H, 7.4; N, 6.9; S, 31.9. Found: C, 54.1; H, 7.6; N, 7.1; S, 32.4.

Example 7.3-(beta-phenylethyl) -2-thiaz0lidinethi0ne H2CN With external cooling, 38 parts of carbon dissulfide is added gradually to 412 parts of 2-(beta-phenylethyl amine)ethanol. A mixture of 24 parts of the white, crystalline product (M.P. 113-114 C.) and 38 parts carbon disulfide is heated in an autoclave at 140 C. for 4 hours. After removal of the excess carbon disulfide by distillation, the residue is purified by crystallization from alcohol. The product, a pale yellow, crystalline material, melts at 73.574 C.

Analysis.Calcd. for C H NS C, 59.1; H, 5.9; N, 6.3; S, 28.7. Found: C, 59.2; H, 5.64; N, 6.47; S, 29.6.

Example 8.3- (1 -naphthylmethyl -2-t'hiaz0lidinethi0ne A mixture of 57 parts of carbon disulfide and 41.7 parts 0 of 2-(l-naphthylmethylamino)ethanol is heated in an autoclave at C. for 3 hours. After crystallization from alcohol, the product consists of colorless crystals melting at 121.5-122 C.

Analysis.Calcd. for C H NS C, 64.8; H, 5.02; N, 5.40; S, 24.7. Found: C, 65.0; H, 4.09; N, 5.53; S, 24.8.

Example 9.3- (Z-farfuryl -2-thiaz0lidinethione A mixture of 38 parts of carbon disulfide and 31.8 parts of 2-(2-furfurylarnino)ethanol is heated in an autoclave for 2 hours at 120 C. The product, after crystallizing from ethanol, consists of colorless crystals melting at 69-70 C.

Analysis.Calcd. for C H NOS C, 48.2; H, 4.52; N, 7.04; S, 32.2. Found: C, 48.0; H, 4.58; N, 6.84; S, 32.7.

Example 10.-3,3-ethylenebis(Z-Zhiazolidinethione) A mixture of 148 parts of N,N'-bis( beta-hydr0xy ethyl)ethylenediamine and 304 parts carbon disulfide is heated in an autoclave at C. for 4 hours. After cooling, the viscous lower layer is separated and is mixed with 800 parts of acetone. The resulting crystalline product is filtered off. After recrystallization from o-dichlorobenzene, the product consists of cream-colored needles melting at 253254 C.

Analysis.Calcd. for C H N S C, 36.4; H, 4.50; N, 10.6; S, 48.5. Found: C, 36.8; H, 4.28; N, 10.0; S, 48.5.

Example 11.3-is0butyl-2-thiaz0lidinethi0ne While cooling, add 45.6 parts of carbon disulfide to 35.0 parts of 2-(isobutylamino)ethanol. The resulting mixture is heated in an autoclave at 120 C. for 3 hours. The crude oily reaction product is stirred with 200 parts of Water. The water insoluble oil is then extracted with ether, and the ether is removed by distillation. By distilling the residue in vacuo, a yellow oil boiling at 178-185 C. at 67 mm. of mercury pressure is obtained.

Analysis.Calcd. for C H NS C, 48.0; H, 7.40; N, 8.00. Found: C, 47.5; H, 7.56; N, 7.80.

For purposes of comparison, in addition to the new compounds shown in Examples 1l1, the derivatives of Z-thiazolidinethione shown in Table I were prepared. These compounds have been previously reported in the chemical literature, and in Table I the melting points found are compared with the melting points given in the references.

TABLE I Derivative 012- Melting Point, C. thiazolidinethione Reference Found Cited 3 benzyl J. Am. Chem. Soc. 78, 61S9 132-133 132. 133 3-(p-chlorobenzyl). J. Am. Chem. Soc. 78, 6191 124-126 125-126 3-n1ethyl J. Chem. Soc. 1949, 786 69-70 68-69 3-n-butyl... (an oil) (an oil) 3-pl1enyl. 131-13 134 -p-tolyl Ber. 15, 1314 105 105 Example 12 TABLE H In the following illustrative examples of the use of the compounds of this invention in a typical black stock, a g ggg gg master batch of polychloroprene (type W) is prepared 0 0 e b 1 i 0 t N r e 1 ill Scorch, minutes 10 26' 3 g i 0 p Op W on two I m 300% Modulus (p.s.i.)- 1,450 1,365 at 0 C. T ereto In t 6 following Order 13 added. gfmprfzssliou Set (Fer- 3 1113)) 4], 41. ress e axation percent 12 parts of phenyl-fi-naphthylamine u g n zuonum 26.1 20. s ongation 26.1 22.1 12 Parts of h,ght'ca,1cmed Mgo Tensile trength at Break (p 3,100 3, 160 parts of Zinc oxide Elongation at Break (percent) 505 515 174 parts of reinforcing black 3 parts of stearic acid Example 13 Two samples, each of 400 parts of the master batch of Example 12 are separately placed on a 2-ro1ler mill, the front and back rolls having temperatures of and 75 C., respectively. To the first is added 1.45 parts of 3- As shown in Table II, polychloroprene compounded with 3-benzyl-2-thiazolidinethione is superior in scorch resistance and stress relaxation and is equal in tensile modulus and compression set properties to that compounded with the commercially-available Z-mercaptoimidazoline previously considered as the best available agent.

Example 14 The procedure of Example 13 is followed substituting equal amounts of other 3-substituted Z-thiazolidinethiones for the 3-benzyl-2-thiazolidinethione. Illustrative results are shown in Table III. As may be seen therefrom, the Z-thiazolidinethiones of this invention are much superior to Z-mercaptoirnidazoline in scorch resistance.

TAB LE III Tensile Strcss Relaxa- Derivative of Scorch, 200% Modulus, 300% Modulus, Elongation at Strength tion, 75% Compression 2thiazolidinethione min. p.s.i. p.s.i. Break, p.s.i. at Break, Elong, Set, percent p.s.i. percent 3-methyl 16 800 1, 650 440 2, 900 11. 1 27. 1 B-ethyl 16 725 1,525 510 3, 275 21. 7 30.0 3phenyl. 24 700 1, 475 500 3, 125 25. 3 34. 5 3-cyelohexy1 22 675 1, 400 520 3, 250 23. 6 40. 3 3p-ehlorophenyl 26 600 1, 150 570 3, 250 29. 3 40. 6 B-p-methoxybenzyl. 25 600 1, 300 520 3, 100 25. 4 3,34athy1enebis 26 650 1,375 500 3, 050 Z-mercaptoimidazoline 8 625 l, 350 550 3, 325 23. 8 32. 5

benzyl-2-thiazolidinethione over 0.5 minute. To the sec- 0nd an equal amount of 2-rnercaptoimidazoline (ethylene thiourea) is added as the accelerator, replacing the 3- benzyl-2-thiazolidinethione. The samples are milled for 23 minutes, conditioned at 73 C. and 61% relative humidity for about 18 hours and then cured at 153 C. for 20 minutes. Both resultant vulcanized rubbers are then subjected to various standard tests to determine their comparative physical characteristics.

The scorch point is determined as the time in minutes at which the viscosity of the unvulcanized rubber reached a value of 5 Mooney units above the minimum, as measured on a Mooney viscometer by ASTM designation D1077-T, at a temperature of 250 F.

The tensile properties of the vulcanized rubber, namely modulus or stress, percent elongation and stress relaxation or tension set, are measured by the procedures of ASTM designation D4l2-51T. The stress relaxation is the increase in length expressed as percent of the original length when rubber is stretched and released.

The compression set of the vulcanized rubber is measured by the procedure of ASTM designation D395-53T using a 30% compression for five hours at 100 C. Compression set is the amount (percent) by which a standard test piece fails to return to its original thickness after being subjected to a standard compressive load for a fixed period of time.

The results of the tests are shown in Table II as the average or two runs for each accelerator.

Preparation of a master batch comprising the polychloroprene and the conventional compounding ingredients is shown above in Example 12. Therein it was noted that the ingredients were added in a specifically designated order. In black stocks, to obtain the delayed action accelerator effect with the vulcanization assistants of the present invention, it is found that optimum results are obtained when the magnesium oxide, the zinc oxide and the carbon black are added in that order. If an antioxidant such as the amine is used, it should be the first added. Addition of stearic acid or other fatty acid to improve distribution of the carbon black should follow the latter. The following examples illustrate this point.

Example 15 Preparation of batches as in Example 12 is repeated a number of times, on a two roller mill at about 50 0, adding to 600 parts of polychloroprene (type W), the same conventional compounding ingredients, identified as follows, but varying the order of addition.

A. 12 parts of phenyl-beta-naphthylamine B. 12 parts of light-calcined magnesium oxide C. 30 parts of zinc oxide D. 174 parts of reinforcing black E. 3 parts of stearic acid.

Thereafter, with the front roll at about 45 C. and the back roll at about 75 C., to 400 part samples of the soprepared batches over about 0.5 minutes is added 1.45

9 parts of 3-benzyl-Z-thiazolidinethione and the mix is milled for 23 minutes. It is then conditioned at 73 C. and about 60% relative humidity for about 18 hours and then cured at 153 C. for twenty minutes. The effect of varying the order of addition on the scorch time and modulus is il- 10 Example 19 The procedure of Example 18 was repeated on the same stock but using varied amounts of accelerator. Illustrative results are shown in the following Table VI.

lustrated 1n the following table. TABLE VI Cured at 307 F. TAB LE IV Accelerator 1 Concentration (parts/ Order of Addition 100 parts of elastomer) 0. 45 0. 65 0. 90 Scorch Modulusat Mooney Scorch, 250 F., (MS), min 19 17 16 1 2 3 4 5 (m 300% (p'.s .i.) Hardness (Shore D):

20 min. cure 60 67 69 E A B C D 42 775 40 min. cure 65 69 71 E B O D A 36 775 Modulus at 300% (p.s.i.): B O D E A 33 880 2 11. cure. 300 425 400 C D B A E 1 40 min. cure- 400 450 875 E C D B A 5 1, 125 Tensile Strength E A C D B 5 1, 050 5 20 min. cure 1, 500 1, 375 1, 250 E A B D C 39 1, 200 40 min. cure 1, 400 1, 300 1, 175 E B D C A 44 Elongation (percent): B D C E A 52 1,150 20 min. cure 910 740 660 D C B A E 1 40 min. cure 760 690 610 E D C B A 1 1,050 Compression Set (percen E A D O B 1 cure 79 47. 7 37. 3

20 B-methyl-Z-thiazplidinethione. o Example 16 Specimen conditioned at 30% compression for 70 hrs. at 100 C.

Repeating Example 15, substituting 3-methyl-2-thiazolidinethione for the 3-benzyl-compound showed the same effect of varying the order of addition.

Example 17 Repeating Example 15, using as the accelerator the Z-mercaptoimidazoline used for comparative purposes in Example 12 as the accelerator showed no substantial effect on the vulcanized product was produced by changing the order of addition.

The reasons for this effect of the order of addition of conventional compounding ingredients before adding the accelerator of this invention are not wholly understood. It is highly surprising. Nevertheless, it is a precaution that should be observed to obtain optimum results.

Although the foregoing examples have been concerned with black stocks, the invention is not necessarily limited thereto. It is equally useful in light-colored or white stocks. This is illustrated in the'following examples.

Example 18 Using the general milling procedure of Examples 12 and 13, a white stock formulation of the following general composition was prepared:

Samples comprising 400 parts of the base stock are cured at 307 F. for varying lengths of time. The time of cure and the physical properties are shown in the following Table V.

TABLE V Scorch (250 F.) Minutes to 5 point rise Curing Time (minutes) 300% Modulus (p.s.i.) 400 425 375 Compression Set (percent) 44. 7 Elongation (percent) 750 610 610 Tensile Strength (p.s.i.) 1, 275 1, 175 1, 150 Aging Test (7 days at 121 0.):

Tensile Strength (p.s.i.) 1, 125 950 950 Elongation (percent) 300 300 300 In the foregoing discussion polychloroprene has been taken as illustrative. As noted above, however, the vulcanization procedure of this invention is applicable also to other synthetic elastomers containing active chlorine. In addition to supplying sites for cross-linking, the chlorine enhances the activity of the double bonds of such polymers or copolymers.

In general, somewhat more accelerator will be used with such chlorine-containing elastomers than for polychloroprene. In general, from about 0.3 to about 10.0 weight percent of the accelerator based on the weight of the chlorine-containing elastomer is employed. In most cases, it will be found preferable to use from about 0.4 to about 6.0 percent. As in the case of polychloroprene, the accelerator may be used in conjunction with conventional compounding ingredients used in the preparation of elastomer vulcanizates.

One such copolymer, shown in US. Patent No. 2,944,- 578, is chlorinated butyl rubber, commonly called chlorobutyl, prepared by chlorinating isobutylene-isoprene copolymers so that the chlorine is introduced predominantly by substitution. Little of the unsaturation originally present in the copolymer is lost. A portion of one of the possible structures for chlorobutyl is shown below. The reactive part of the molecule is enclosed in brackets.

' L 1 CH3 01 CH:

One such product is commercially available under the designation Enjay Butyl HT 106 6 which contains some 1.1 and 1.3% chlorine or about one atom of chlorine per double bond. Unsa-turation is 1-2 mol percent. The product also contains 0.1-0.2% of inhibitor (2,6-di-t-butyl-4- methyl phenol). This product will be taken as illustra tive. Commercially-purchased samples thereof were utilized in the examples set out below.

Two types of vulcanization are possible in the case of chlorobutyl. One type, vulcanization in conventional sulfur systems, is believed to take place through the double bond. In the other type, vulcanization with zinc oxide, amines, phenols and the like, curing is believed to take place through cross-linking at the carbons carrying th chlorine.

Zinc oxide alone cures chlorobutyl by acting through the active chlorine atoms. However, the cure is relatively slow and the tensile strength and modulus of so-cured products are lower than can be obtained by other cure systems. For example, addition of tetramethyl thiuram disulfide, presumably causing sulfur to react at the unsaturated carbon atoms to give sulfur-to-carbon bridges, speeds up the zinc oxide cure. Unfortunately, such practice results in compounded stocks which are scorchy.

(Scorch time is extended if benzothiazyl disulfide also is added. In general, this type of cure gives products with the best all-round properties and is the basic cure system generally recommended for industrial practice.

Primary amines, such as diethylene triamine, will cure chlorobutyl by cross-linking at the chlorine atoms. The cure also is slow unless acid acceptors, such as magnesium oxide, are used. Again, unfortunately the cure then tends to be too scorchy. Shelf-life of so-compounded stocks is low. Zinc oxide is not required. Z-mercaptoimidazoline (ethylene thiourea) cures chlorobutyl much like amines, but gives better physical properties, and is less scorchy and easier to handle. This is particularly true for lightcolored mineral-filled compounds. The cure with 2- rnercaptoimidazoline is scorchy with carbon black-filled compounds. The manufacturers recommended curing systems using 2-rnercaptoimidazoline contain benzothiazyl disulfide, magnesium oxide and zinc oxide.

Example 20 In order to illustrate the desirable faster curing rate of the thiazolidinethiones of this invention as compared with the conventionally recommended ethylene thiourea, noted above, the test compositions shown below were prepared using the latter and the 3-methyl-2-thiazolidinethione of this invention, respectively, as accelerators.

Component: Parts Chlorobutyl elastomer 100 Stearic acid 1 Magnesium oxide 1 High abrasion furnace black 50 Zinc oxide 5 Accelerator 2 12 Example 22 A sample of chlorosulfonated polyethylene elastomer commercially available as Hypalon was procured; compounded as in Example 21; and cured for 60 minutes at 141 C. The formulation and physical properties of the resultant products are shown in the following Table VIII.

TABLE VIIL-FORMULATION Properties:

Mooney scorch-min., 287 F. (TA5) 1.2 Hardness, Shore 65 Modulus, 300% 475 Tensile strength (p.s.i. 675 Elongation, percent 420 1 N o cure.

Example 23 The general procedure of Example 22 was repeated on an elastomeric copolymer of ethyl acrylate and vinyl chloroacetate. Curing was for minutes at 160 0, followed by heating for 24 hours at 150 C. The formulation and properties of the resulting vulcanizates are shown in the following Table IX.

TABLE IX.FORMULATION Thereafter the Mooney scorch time at 260 F. to a 5 point Parts rise was determined for each. The time of 49 minutes A B with the ethylene thiourea was reduced to only 14 min- 0 t ornponent: utcs with the 3 methyl 2 thlazolldinethione. Acrylic elastomer 100 100 gteam i i t "151 l; 5 5% I elm-rem 0T0 ng urnace 3G Example 21 Magnesium oxide 1 1 P 3-nzethyl-2-thiazolidinethione 2 roper res: The following stock formulations were prepared using Mooney scorch (mm), F (TM) 7 60 the general procedure of Examples 12 and 13 and the fiarg r res gggrrz A..

0 us, p.s1 elastomer of Example 20. Modulu 200% (p- 975 Tenslle Strength (p.s 1, 825 Elongation (pereent). 400 Component Part5 Compression set 80 A B C i N 0 cure.

Elastorner 100 100 100 High abrasion furnace black- 25 25 25 5O gast gtrusion furnace black. 25 25 25 ara n 1 1 1 Mineral oil e 6 6 Example 24 2,2t)-ri1e1th31 llene1ais(4-methyl-6tert.- 1 1 1 11 V 8110 Zinc f 5 5 5 The general procedure of Example 22 was repeated on Magnesium oxide 1. 0 3 methyl 2 thiamndinethione 1.0 L0 an ethyl y e nd h e yl vmyl her el s omenc Mogney scorch at F4115) 425 25 m3 copolymer commercially available under the designation (minutes) The resultant compositions were cured at 307 F. for 30 minutes and thereafter the physical properties of the vulcanizates was determined. Illustrative results are shown in the following Table VII.

These results show that 3-rnethyl-2-thiazolidinethione has strong accelerating activity on the vulcanization of chlorobutyl rubber with zinc oxide. Also, it will be seen from Sample C that the scorch time is extended by using magnesium oxide in the rubber composition.

Hycar 4021 as shown in the following Table X.

TABLE X.FORMULATION Parts Component A B 100 i 0. 5 0. 5 40 40 Magnesium oxide. 5 5 Dlphenylguanidlne- 3 3 ur 2 2 8-rnethyl-2-thlazolidinethione 5 Thereafter the Mooney scorch time at 287 F. to a 5 point rise was determined for each elastomer composition. The time of 20 minutes with no accelerator was reduced to only 12 minutes with the 3-methyl-2-thiazoli- .dinethione.

13 Example 25 The following rubber compositions were compounded using equivalent amounts of magnesium and calcium oxides:

Parts by Weight Neoprene W 100 100 Steuric Acid 0. 5 0.5 Magnesium Oxide. 4 Calcium Oxide 5. 8 Phenyl-beta-naphthylaml 2 2 Carbon Black SRF... 29 29 Zinc Oxide 5 5 3-n1ethyl-2-thiazolidinethione 0. 5 0.5

The scorch points and curing data as determined on a Monsanto rheometer are as follows:

Scorch, min 15. 19. 3 Monsanto Rheometer:

Max. Torque, in. lb 77. 2 73.1 95% Torque, in. lb 73. 4 69. 6 95% total cure, min 15.0 10.

wherein R is alkyl, hydroxyalkyl or alkoxyalkyl of from 1-6 carbons; cyclohexyl; phenyl, naphthyl, chloro-, alkylor alkoxy-substituted phenyl and naphthyl; aralkyl; furfuryl or morpholinoalkyl; and R is alkylene of 1-4 carbons, phenylene or cyclohexylene.

Z. The composition according to claim 1 containing an effective amount of an alkaline earth metal oxide to serve as an acid binder during vulcanization.

3. A composition according to claim 1 in which said elastomer is a copolymer of ethyl acrylate and vinyl chloroacetate.

4. The vulcanizable composition of claim 1 comprising from about 0.1 to about 1.0 weight percent, based on the polymer, of 3-methyl-2-thiazolidinethione.

5. The composition of claim 2 containing as a curing agent, an effective amount of zinc oxide.

6. The composition of claim 1 wherein the elastomer is polychloroprene.

7. The composition of claim 1 wherein the elastomer is chlorobutyl.

No references cited.

JOSEPH L. SCHOFER, Primary Examiner.

D. K. DENENBERG, Assistant Examiner. 

1. A VULCANIZABLE COMPOSITION COMPRISING AN UNVULCANIZED, VULCANIZABLE ACTIVE CHLORINE-CONTAINING ELASTOMER, AND FROM ABOUT 0.1 TO ABOUT 2.5 WEIGHT PERCENT, BASED ON THE POLYMER, OF AN ACCELERATOR OF THE FORMULA: 